Compositions and Methods for Activating Titanium Substrates

ABSTRACT

A method for pretreating a substrate prior to depositing a material thereon, the method including immersing the substrate in an activation solution for a predetermined period of time, the activation solution including an ammonium salt that includes a fluorine-containing anion, sulfuric acid and water.

FIELD

This application relates to material deposition onto substrates and,more particularly, to compositions and methods for activating metallicsubstrates and compositions and methods for electrodepositingtin-bismuth alloys onto metallic substrates.

BACKGROUND

Mechanical fasteners are widely used for joining two or more componentsof a structural assembly. For example, mechanical fasteners areextensively used for joining the structural components of the airframeof an aircraft.

Aircraft experience electromagnetic effects (EME) from a variety ofsources, such as lightning strikes and precipitation static. Metallicaircraft structures are readily conductive and, therefore, arerelatively less susceptible to electromagnetic effects. However,composite (e.g., carbon fiber reinforced plastic) aircraft structures donot readily conduct away the significant electrical currents andelectromagnetic forces stemming from electromagnetic effects. Therefore,when mechanical fasteners are used in composite aircraft structures,steps must be taken to protect against electromagnetic effects.

Electromagnetic effects protection can be provided to mechanicalfasteners in the form of an electrically conductive metallic surfacedeposit, such as metallic plating. While various metallic surfacedeposits may provide suitable electrical conductivity for impartingelectromagnetic effects protection, other factors, such as lubricity andgalvanic compatibility with carbon fiber-reinforced plastics, are alsoconsiderations for mechanical fasteners intended for the aerospaceindustry.

Tin exists in alpha and beta phases. Alpha tin is grey in color, powderyand forms pest, while beta tin is white and possesses body centeredtetragonal crystal structure. When tin is alloyed with bismuth atconcentrations greater than 0.4 percent by weight bismuth, it begins toexist as beta phase. Tin-bismuth has shown promise as a suitablemetallic surface deposit for mechanical fasteners due to its electricalconductivity, lubricity and galvanic compatibility with carbonfiber-reinforced plastics.

Accordingly, those skilled in the art continue with research anddevelopment efforts in the field of electrodeposition.

SUMMARY

An activation solution including water, an ammonium salt having afluorine-containing anion, and sulfuric acid.

An activation solution including water, ammonium bifluoride and/orammonium tetrafluoroborate dissolved in the water, and sulfuric aciddissolved in the water.

An activation solution including water, ammonium bifluoride and/orammonium tetrafluoroborate dissolved in the water at a concentrationranging from about 10 grams per liter to about 150 grams per liter,based on a total volume of the activation solution, and sulfuric aciddissolved in the water at a concentration ranging from about 1 percentby volume to about 70 percent by volume, based on a total volume of theactivation solution.

An activation solution including water, ammonium bifluoride dissolved inthe water at a concentration ranging from about 20 grams per liter toabout 120 grams per liter, based on a total volume of the activationsolution, and sulfuric acid dissolved in the water at a concentrationranging from about 5 percent by volume to about 25 percent by volume,based on a total volume of the activation solution.

A method for manufacturing an activation solution includes steps of (1)mixing sulfuric acid with water to yield an acidic solution and (2)dissolving an ammonium salt in the acidic solution, the ammonium salthaving a fluorine-containing anion.

A method for pretreating a substrate prior to depositing a materialthereon, the method including the step of immersing the substrate in anactivation solution for a predetermined period of time, the activationsolution including water, an ammonium salt dissolved in the water, theammonium salt having a fluorine-containing anion, and sulfuric aciddissolved in the water.

Other expressions of the disclosed compositions and methods foractivating metallic substrates will become apparent from the followingdetailed description, the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram depicting a disclosed method for depositing amaterial onto a substrate;

FIG. 2 is micrograph of a tin-bismuth alloy deposited on a titaniumsubstrate in accordance with the method of FIG. 1;

FIG. 3 is a flow diagram depicting one disclosed method for activating asubstrate, such as a titanium substrate, in accordance with the methodof FIG. 1;

FIG. 4 is a schematic illustration of a system for activating asubstrate in accordance with the method of FIG. 3;

FIG. 5 is a flow diagram depicting another disclosed method foractivating a substrate, such as a titanium substrate, in accordance withthe method of FIG. 1;

FIG. 6 is a schematic illustration of a system for activating asubstrate in accordance with the method of FIG. 5;

FIG. 7 is a flow diagram depicting yet another disclosed method foractivating a substrate, such as a titanium substrate, in accordance withthe method of FIG. 1;

FIG. 8 is a schematic illustration of a system for activating asubstrate in accordance with the method of FIG. 7;

FIG. 9 is a schematic illustration of a system for strike plating asubstrate in accordance with the method of FIG. 1;

FIG. 10 is a flow diagram depicting one disclosed method forelectrodepositing a tin-bismuth alloy onto a substrate in accordancewith the method of FIG. 1;

FIG. 11 is a schematic illustration of an electrodeposition system fordepositing a tin-bismuth alloy in accordance with the method of FIG. 10;

FIG. 12 is a flow diagram of an aircraft manufacturing and servicemethodology; and

FIG. 13 is a block diagram of an aircraft.

DETAILED DESCRIPTION

Disclosed are compositions, systems and methods for activating ametallic substrate, such as a metallic fastener or other part/component.Also disclosed are compositions, systems and methods for depositing amaterial onto a metallic substrate, such as a metallic fastener or otherpart/component. The disclosed compositions, systems and methods may beused separately or in various combinations to achieve the desiredmaterial deposit on a substrate.

Referring to FIG. 1, disclosed is a method, generally designated 10, fordepositing a material onto a substrate. While only three general stepsare shown, those skilled in the art will appreciate that variousadditional steps may be performed—whether before, after or between thepresented steps—without resulting in a departure from the scope of thepresent disclosure.

The initial step (Block 12) of method 10 includes pre-treating thesubstrate to render the substrate suitable for receiving thereon amaterial, such as a metallic deposit or other metallic/non-metallicmaterial. Various pre-treatments may be performed, such as cleaning,degreasing, etching and the like. In particular, the pre-treating step(Block 12) may include activating (Block 14) the surface of thesubstrate. For example, in the case of titanium substrates, the step ofactivating (Block 14) the surface of the substrate may remove (or atleast substantially reduce) the tenacious oxide layer that is known toform thereon.

The intermediate step (Block 16) of method 10 includes strike platingthe pre-treated substrate. The step of strike plating (Block 16) thesurface of the substrate may form a thin metallic layer on the surfaceof the substrate, thereby providing the substrate with a surface moresuitable for receiving and bonding with a subsequent metallic deposit.In a particular implementation, the strike plating step (Block 16) mayform a thin layer of nickel on the surface of the substrate.

The final step (Block 18) of method 10 includes electrodeposition ontothe strike-plated substrate. The electrodeposition step (Block 18) mayform a metallic deposit on the surface of the substrate. In a particularimplementation, the electrodeposition step (Block 18) may deposit atin-bismuth alloy on the surface of the substrate.

Referring to FIG. 2, the disclosed method 10 was used to deposit a thinlayer of a tin-bismuth alloy onto the surface of a titanium alloy(Ti-6Al-4V) substrate. The result was an excellent bond between thetin-bismuth alloy deposit and the underlying titanium alloy substrate.

While the present disclosure primarily focuses on titaniumsubstrates-substrates formed from titanium or titanium alloys, such asTi-6Al-4V, it is believed that the disclosed method 10, as well asindividual steps of the disclosed method 10 (e.g., the activating step(Block 14), the strike plating step (Block 16) and/or theelectrodeposition step (Block 18)) may be suitable for non-titaniumsubstrates. Examples of non-titanium substrates that may benefit fromthe present disclosure include, without limitation, iron alloys, copperalloys and nickel alloys (e.g., Inconel).

Activation

Disclosed are three activation methods, including associatedcompositions and systems. A metallic substrate, such as a titaniumsubstrate, may be activated using just one of the disclosed activationmethods. Alternatively, a metallic substrate, such as a titaniumsubstrate, may be activated using multiple activation methods (e.g., asequence of activation methods), including one or more of the disclosedactivation methods.

Referring to FIGS. 3 and 4, a first activation method, generallydesignated 100, may begin at Block 110 (FIG. 3) with the step ofpreparing a bath 152 containing an activation solution 154, as shown inFIG. 4. The bath 152 and the activation solution 154 may comprise thefirst activation system 150.

The bath 152 may be any vessel suitable for receiving and containing theactivation solution 154. Compositionally, the material forming the bath152 should be chemically compatible with the activation solution 154. Ofcourse, the bath 152 should be sized and shaped to be able to receivetherein the substrate 156 to be activated by the first activation system150.

The activation solution 154 includes water (H₂O), an ammonium saltdissolved in the water, and sulfuric acid (H₂SO₄) dissolved in thewater. The activation solution 154 may be maintained at atmosphericpressure (e.g., 1 atm) and at a temperature between about 15° C. andabout 50° C. (e.g., room temperature (˜21° C.)). However, using higherand lower pressures, and higher and lower temperatures is contemplated,and will not result in a departure from the scope of the presentdisclosure.

The ammonium salt in the activation solution 154 may have afluorine-containing anion. In one formulation, the ammonium salt in theactivation solution 154 is ammonium bifluoride (NH₄HF₂). In anotherformulation, the ammonium salt in the activation solution 154 isammonium tetrafluoroborate (NH₄BF₄). In yet another formulation, theammonium salt in the activation solution 154 includes both ammoniumbifluoride (NH₄HF₂) and ammonium tetrafluoroborate (NH₄BF₄).

The ammonium salt in the activation solution 154 may be present at aconcentration ranging from about 10 grams per liter to about 150 gramsper liter, based on the total volume of the activation solution 154. Inone alternative expression, the ammonium salt concentration ranges fromabout 20 grams per liter to about 120 grams per liter, based on thetotal volume of the activation solution 154. In another alternativeexpression, the ammonium salt concentration ranges from about 30 gramsper liter to about 110 grams per liter, based on the total volume of theactivation solution 154. In another alternative expression, the ammoniumsalt concentration ranges from about 40 grams per liter to about 100grams per liter, based on the total volume of the activation solution154. In another alternative expression, the ammonium salt concentrationranges from about 50 grams per liter to about 100 grams per liter, basedon the total volume of the activation solution 154. In anotheralternative expression, the ammonium salt concentration ranges fromabout 60 grams per liter to about 100 grams per liter, based on thetotal volume of the activation solution 154. In another alternativeexpression, the ammonium salt concentration ranges from about 70 gramsper liter to about 90 grams per liter, based on the total volume of theactivation solution 154. In yet alternative expression, the ammoniumsalt concentration is about 80 grams per liter, based on the totalvolume of the activation solution 154.

The sulfuric acid in the activation solution 154 may be present at aconcentration ranging from about 1 percent by volume to about 70 percentby volume, based on the total volume of the activation solution 154. Inone alternative expression, the sulfuric acid concentration ranges fromabout 2 percent by volume to about 50 percent by volume, based on thetotal volume of the activation solution 154. In another alternativeexpression, the sulfuric acid concentration ranges from about 3 percentby volume to about 40 percent by volume, based on the total volume ofthe activation solution 154. In another alternative expression, thesulfuric acid concentration ranges from about 4 percent by volume toabout 30 percent by volume, based on the total volume of the activationsolution 154. In another alternative expression, the sulfuric acidconcentration ranges from about 5 percent by volume to about 25 percentby volume, based on the total volume of the activation solution 154. Inanother alternative expression, the sulfuric acid concentration rangesfrom about 5 percent by volume to about 15 percent by volume, based onthe total volume of the activation solution 154. In yet anotheralternative expression, the sulfuric acid concentration is about 10percent by volume, based on the total volume of the activation solution154.

As one specific, non-limiting example, the activation solution 154includes water, 80 grams per liter ammonium bifluoride (NH₄HF₂), and 10percent by volume sulfuric acid (H₂SO₄).

The activation solution 154 may be manufactured in various ways withoutdeparting from the scope of the present disclosure. In one particularimplementation, the disclosed method for manufacturing the activationsolution 154 includes steps of (1) mixing sulfuric acid (e.g., 66 degreeBaume sulfuric acid) with water (e.g., deionized water) to yield anacidic solution, (2) dissolving an ammonium salt (e.g., ammoniumbifluoride and/or ammonium tetrafluoroborate) in the acidic solution;and (3) adding additional water, if needed, to make up the requiredtotal volume of the activation solution 154.

At Block 120 (FIG. 3), the substrate 156 is immersed (e.g., completelyimmersed) in the activation solution 154. The substrate 156 may remainimmersed in the activation solution 154 for a predetermined period oftime prior to removing the substrate 156 from the activation solution154, as shown in Block 130 (FIG. 3). In the case of titanium substrates(substrate 156), the predetermined period of time may be selected suchthat the activation solution 154 has sufficient time to reduce/eliminatethe tenacious oxide layer on the substrate 156 without significantlydisturbing the titanium/titanium alloy underlying the oxide layer. Inone expression, the predetermined period of time is about 5 seconds toabout 120 seconds. In another expression, the predetermined period oftime is about 10 seconds to about 100 seconds. In another expression,the predetermined period of time is about 20 seconds to about 40seconds. In yet another expression, the predetermined period of time isabout 30 seconds.

At Block 140 (FIG. 3), the substrate 156 removed from the activationsolution 154 may be rinsed with a rinsing fluid. As an example, therinsing fluid may be water, such as deionized water.

Referring to FIGS. 5 and 6, a second activation method, generallydesignated 200, may begin at Block 202 (FIG. 5) with the step ofpreparing a bath 252 containing an activation solution 254, as shown inFIG. 6. The bath 252 and the activation solution 254 may comprise thesecond activation system 250.

The bath 252 may be any vessel suitable for receiving and containing theactivation solution 254. Compositionally, the material forming the bath252 should be chemically compatible with the activation solution 254. Ofcourse, the bath 252 should be sized and shaped to be able to receivetherein the substrate 256 to be activated by the second activationsystem 250.

The activation solution 254 includes water (H₂O), a fluoride saltdissolved in the water, hydrofluoric acid (HF) dissolved in the water,and sulfuric acid (H₂SO₄) dissolved in the water. The activationsolution 254 may be maintained at atmospheric pressure (e.g., 1 atm) andat a temperature between about 15° C. and about 50° C. (e.g., roomtemperature (˜21° C.)). However, using higher and lower pressures, andhigher and lower temperatures is contemplated, and will not result in adeparture from the scope of the present disclosure.

The fluoride salt in the activation solution 254 may have an alkalimetal cation and/or an alkaline earth metal cation. In one formulation,the fluoride salt in the activation solution 254 is potassium fluoride(KF). In another formulation, the fluoride salt in the activationsolution 254 is lithium fluoride (LiF). In another formulation, thefluoride salt in the activation solution 254 is sodium fluoride (NaF).In another formulation, the fluoride salt in the activation solution 254is rubidium fluoride (RuF). In another formulation, the fluoride salt inthe activation solution 254 is barium fluoride (BaF₂). In anotherformulation, the fluoride salt in the activation solution 254 isstrontium fluoride (SrF₂). In yet another formulation, the fluoride saltin the activation solution 254 includes at least two of potassiumfluoride (KF), lithium fluoride (LiF), sodium fluoride (NaF), rubidiumfluoride (RuF), barium fluoride (BaF₂), and strontium fluoride (SrF₂).

The fluoride salt in the activation solution 254 may be present at aconcentration ranging from about 5 grams per liter to about 120 gramsper liter, based on the total volume of the activation solution 254. Inone alternative expression, the fluoride salt concentration ranges fromabout 10 grams per liter to about 100 grams per liter, based on thetotal volume of the activation solution 254. In another alternativeexpression, the fluoride salt concentration ranges from about 15 gramsper liter to about 75 grams per liter, based on the total volume of theactivation solution 254. In another alternative expression, the fluoridesalt concentration ranges from about 15 grams per liter to about 50grams per liter, based on the total volume of the activation solution254. In another alternative expression, the fluoride salt concentrationranges from about 15 grams per liter to about 30 grams per liter, basedon the total volume of the activation solution 254. In yet alternativeexpression, the fluoride salt concentration is about 20 grams per liter,based on the total volume of the activation solution 254.

The hydrofluoric acid in the activation solution 254 may be present at aconcentration ranging from about 5 milliliters per liter to about 250milliliters per liter, based on the total volume of the activationsolution 254. In one alternative expression, the hydrofluoric acidconcentration ranges from about 10 milliliters per liter to about 200milliliters per liter, based on the total volume of the activationsolution 254. In another alternative expression, the hydrofluoric acidconcentration ranges from about 15 milliliters per liter to about 150milliliters per liter, based on the total volume of the activationsolution 254. In another alternative expression, the hydrofluoric acidconcentration ranges from about 20 milliliters per liter to about 150milliliters per liter, based on the total volume of the activationsolution 254. In another alternative expression, the hydrofluoric acidconcentration ranges from about 30 milliliters per liter to about 100milliliters per liter, based on the total volume of the activationsolution 254. In another alternative expression, the hydrofluoric acidconcentration ranges from about 40 milliliters per liter to about 80milliliters per liter, based on the total volume of the activationsolution 254. In yet another alternative expression, the hydrofluoricacid concentration is about 60 milliliters per liter, based on the totalvolume of the activation solution 254.

The sulfuric acid in the activation solution 254 may be present at aconcentration ranging from about 1 percent by volume to about 45 percentby volume, based on the total volume of the activation solution 254. Inone alternative expression, the sulfuric acid concentration ranges fromabout 2 percent by volume to about 35 percent by volume, based on thetotal volume of the activation solution 254. In another alternativeexpression, the sulfuric acid concentration ranges from about 2 percentby volume to about 20 percent by volume, based on the total volume ofthe activation solution 254. In another alternative expression, thesulfuric acid concentration ranges from about 3 percent by volume toabout 15 percent by volume, based on the total volume of the activationsolution 254. In another alternative expression, the sulfuric acidconcentration ranges from about 3 percent by volume to about 10 percentby volume, based on the total volume of the activation solution 254. Inyet another alternative expression, the sulfuric acid concentration isabout 5 percent by volume, based on the total volume of the activationsolution 254.

As one specific, non-limiting example, the activation solution 254includes water, 20 grams per liter potassium fluoride (KF), 60milliliters per liter hydrofluoric acid (HF), and 5 percent by volumesulfuric acid (H₂SO₄).

The activation solution 254 may be manufactured in various ways withoutdeparting from the scope of the present disclosure. In one particularimplementation, the disclosed method for manufacturing the activationsolution 254 includes steps of (1) mixing sulfuric acid (e.g., 66 degreeBaume sulfuric acid) with water (e.g., deionized water) to yield a firstacidic solution, (2) mixing hydrofluoric acid (e.g., 48 wt % in water)with the first acidic solution to yield a second acidic solution, (3)dissolving a fluoride salt (e.g., potassium fluoride) in the secondacidic solution; and (4) adding additional water, if needed, to make upthe required total volume of the activation solution 254.

At Block 204 (FIG. 5), the substrate 256 is immersed (e.g., completelyimmersed) in the activation solution 254. The substrate 256 may remainimmersed in the activation solution 254 for a predetermined period oftime prior to removing the substrate 256 from the activation solution254, as shown in Block 206 (FIG. 5). In the case of titanium substrates(substrate 256), the predetermined period of time may be selected suchthat the activation solution 254 has sufficient time to reduce/eliminatethe tenacious oxide layer on the substrate 256 without significantlydisturbing the titanium/titanium alloy underlying the oxide layer. Inone expression, the predetermined period of time is about 5 seconds toabout 120 seconds. In another expression, the predetermined period oftime is about 10 seconds to about 100 seconds. In another expression,the predetermined period of time is about 20 seconds to about 40seconds. In yet another expression, the predetermined period of time isabout 30 seconds.

At Block 208 (FIG. 5), the substrate 256 removed from the activationsolution 254 may be rinsed with a rinsing fluid. As an example, therinsing fluid may be water, such as deionized water.

Referring to FIGS. 7 and 8, a third activation method, generallydesignated 300, may begin at Block 302 (FIG. 7) with the step ofpreparing a bath 352 containing an activation solution 354, as shown inFIG. 8. The bath 352 and the activation solution 354, together with agraphite electrode 358 and current source 360, may comprise the thirdactivation system 350, which may be used to perform an anodic sulfuricacid method (third activation method 300), as is described herein.

The bath 352 may be any vessel suitable for receiving and containing theactivation solution 354. Compositionally, the material forming the bath352 should be chemically compatible with the activation solution 354. Ofcourse, the bath 352 should be sized and shaped to be able to receivetherein the graphite anode 358 and the substrate 356 to be activated bythe third activation system 350.

The activation solution 354 includes water (H₂O) and sulfuric acid(H₂SO₄) dissolved in the water. The activation solution 354 may bemaintained at atmospheric pressure (e.g., 1 atm) and at a temperaturebetween about 15° C. and about 50° C. (e.g., room temperature (˜21°C.)). However, using higher and lower pressures, and higher and lowertemperatures is contemplated, and will not result in a departure fromthe scope of the present disclosure.

The sulfuric acid in the activation solution 354 may be present at aconcentration ranging from about 5 percent by volume to about 45 percentby volume, based on the total volume of the activation solution 354. Inone alternative expression, the sulfuric acid concentration ranges fromabout 5 percent by volume to about 35 percent by volume, based on thetotal volume of the activation solution 354. In another alternativeexpression, the sulfuric acid concentration ranges from about 5 percentby volume to about 30 percent by volume, based on the total volume ofthe activation solution 354. In another alternative expression, thesulfuric acid concentration ranges from about 5 percent by volume toabout 25 percent by volume, based on the total volume of the activationsolution 354. In another alternative expression, the sulfuric acidconcentration ranges from about 10 percent by volume to about 20 percentby volume, based on the total volume of the activation solution 254. Inyet another alternative expression, the sulfuric acid concentration isabout 15 percent by volume, based on the total volume of the activationsolution 354.

As one specific, non-limiting example, the activation solution 354includes water and 15 percent by volume sulfuric acid (H₂SO₄).

At Block 304 (FIG. 7), the substrate 356 is immersed (e.g., completelyimmersed) in the activation solution 354. A lead 368 may electricallycouple the immersed substrate 356 with a first terminal 364 of thecurrent source 360.

At Block 306 (FIG. 7), the graphite electrode 358 is immersed (e.g.,completely immersed) in the activation solution 354. A lead 366 mayelectrically couple the immersed graphite electrode 358 with a secondterminal 362 of the current source 360.

At Block 308 (FIG. 7), the current source 360 is actuated such that anelectric current is passed between the substrate 356 and the graphiteelectrode 358. The current source 360 may be configured such that thesubstrate 356 functions as the anode, thereby etching the substrate 356.In the case of titanium substrates (substrate 356), the anodic sulfuricacid method (third activation method 300) may reduce/eliminate thetenacious oxide layer on the substrate 356 without significantlydisturbing the titanium/titanium alloy underlying the oxide layer.

The step of passing an electric current (Block 308) may be performed atvarious current densities without departing from the scope of thepresent disclosure. Those skilled in the art will appreciate thatcurrent density is a controllable parameter, and selection of anappropriate current density may require consideration of variousfactors, such as the duration of the passing step (Block 308), amongother factors. In one expression, the electric current passed during thepassing step (Block 308) may have a current density ranging from about10 amperes per square foot to about 80 amperes per square foot, based onthe surface area of the substrate 356. In another expression, theelectric current passed during the passing step (Block 308) may have acurrent density ranging from about 20 amperes per square foot to about60 amperes per square foot, based on the surface area of the substrate356. In another expression, the electric current passed during thepassing step (Block 308) may have a current density ranging from about20 amperes per square foot to about 40 amperes per square foot, based onthe surface area of the substrate 356. In yet another expression, theelectric current passed during the passing step (Block 308) may have acurrent density of about 30 amperes per square foot, based on thesurface area of the substrate 356.

The step of passing an electric current (Block 308) may be performed forvarious durations of time without departing from the scope of thepresent disclosure. Those skilled in the art will appreciate that thecurrent duration is a controllable parameter, and selection of anappropriate duration of time may require consideration of variousfactors, such as the current density, among other factors. In oneexpression, the passing step (Block 308) may be performed for about 5seconds to about 120 seconds. In another expression, the passing step(Block 308) may be performed for about 10 seconds to about 100 seconds.In another expression, the passing step (Block 308) may be performed forabout 10 seconds to about 60 seconds. In another expression, the passingstep (Block 308) may be performed for about 15 seconds to about 45seconds. In yet another expression, the passing step (Block 308) may beperformed for about 20 seconds to about 30 seconds.

At Block 310 (FIG. 7), the substrate 356 is disconnected from thecurrent source 360 and removed from the activation solution 354.

At Block 312 (FIG. 7), the substrate 356 may be rinsed with a rinsingfluid. As an example, the rinsing fluid may be water, such as deionizedwater.

Strike Plating

Various strike plating processes, including nickel strike platingprocesses (e.g., Wood's nickel strike) are known in the art, and may beused in the method 10 of FIG. 1 without departing from the scope of thepresent disclosure. However, disclosed is a particular nickel strikeplating method that yielded an excellent substrate-to-subsequent platingbond, as shown in FIG. 2.

Referring to FIG. 9, a strike plating system, generally designated 450,includes a bath 452, an electrolyte solution 454 received in the bath452, a nickel anode 458 immersed in the electrolyte solution 454, andcurrent source 460. The current source 460 may include first terminal462 and a second terminal 464. The nickel anode 458 may be electricallycoupled with the second terminal 464 by way of a lead 468.

The bath 452 may be any vessel suitable for receiving and containing theelectrolyte solution 454. Compositionally, the material forming the bath452 should be chemically compatible with the electrolyte solution 454.Of course, the bath 452 should be sized and shaped to be able to receivetherein the substrate 456 and the nickel anode 458.

The electrolyte solution 454 includes water (H₂O), nickel chloride(NiCl₂) dissolved in the water, and hydrochloric acid (HCl) dissolved inthe water. The electrolyte solution 454 may be maintained at atmosphericpressure (e.g., 1 atm) and at a temperature between about 15° C. andabout 50° C. (e.g., room temperature (˜21° C.)). However, using higherand lower pressures, and higher and lower temperatures is contemplated,and will not result in a departure from the scope of the presentdisclosure.

The nickel chloride in the electrolyte solution 454 may be present at aconcentration ranging from about 50 grams per liter to about 400 gramsper liter, based on the total volume of the activation solution 354. Inone alternative expression, the nickel chloride concentration rangesfrom about 75 grams per liter to about 350 grams per liter, based on thetotal volume of the activation solution 354. In another alternativeexpression, the nickel chloride concentration ranges from about 100grams per liter to about 300 grams per liter, based on the total volumeof the activation solution 354. In another alternative expression, thenickel chloride concentration ranges from about 125 grams per liter toabout 275 grams per liter, based on the total volume of the activationsolution 354. In another alternative expression, the nickel chlorideconcentration ranges from about 150 grams per liter to about 250 gramsper liter, based on the total volume of the activation solution 354. Inanother alternative expression, the nickel chloride concentration rangesfrom about 175 grams per liter to about 225 grams per liter, based onthe total volume of the activation solution 354.

The hydrochloric acid in the electrolyte solution 454 may be present ata concentration ranging from about 25 milliliters per liter to about 300milliliters per liter, based on the total volume of the electrolytesolution 454. In one alternative expression, the hydrochloric acidconcentration ranges from about 50 milliliters per liter to about 250milliliters per liter, based on the total volume of the electrolytesolution 454. In another alternative expression, the hydrochloric acidconcentration ranges from about 75 milliliters per liter to about 225milliliters per liter, based on the total volume of the electrolytesolution 454. In another alternative expression, the hydrochloric acidconcentration ranges from about 100 milliliters per liter to about 200milliliters per liter, based on the total volume of the electrolytesolution 454. In another alternative expression, the hydrochloric acidconcentration ranges from about 125 milliliters per liter to about 175milliliters per liter, based on the total volume of the electrolytesolution 454.

As one specific, non-limiting example, the electrolyte solution 454includes water, 200 grams per liter nickel chloride (NiCl₂) and 150milliliters per limiter hydrochloric acid (HCl).

As shown in FIG. 9, the substrate 456 is immersed (e.g., completelyimmersed) in the electrolyte solution 454 in the bath 452. Then, thesubstrate 456 is electrically coupled with the first terminal 462 of thecurrent source 460 by way of a lead 466.

To begin strike plating, the current source 460 is actuated such that anelectric current is passed between the substrate 456 and the nickelanode 458, and a deposit forms on the substrate 456. Optionally, priorto initiating a cathodic strike, an anodic strike (substrate 456functions as the anode) may be performed to etch the substrate 456.

The anodic strike (etching) may be performed at various currentdensities and durations of time without departing from the scope of thepresent disclosure. In one expression, the anodic strike may beperformed at a current density ranging from about 25 amperes per squarefoot to about 75 amperes per square foot, based on the surface area ofthe substrate 456, for a duration ranging from about 1 second to about30 seconds. For example, the anodic strike may be performed at a currentdensity of about 120 amperes per square foot, based on the surface areaof the substrate 456, for about 10 seconds.

The cathodic strike (strike plating) may be performed at various currentdensities and durations of time without departing from the scope of thepresent disclosure. In one expression, the cathodic strike may beperformed at a current density ranging from about 80 amperes per squarefoot to about 160 amperes per square foot, based on the surface area ofthe substrate 456, for a duration ranging from about 30 seconds to about10 minutes. For example, the cathodic strike may be performed at acurrent density of about 120 amperes per square foot, based on thesurface area of the substrate 456, for about 5 minutes.

Once the current source 460 is deactivated, the substrate 456 can bedisconnected from the current source 460 and removed from theelectrolyte solution 454. Then, the substrate 356 may be rinsed with arinsing fluid, such as deionized water.

Electrodeposition

Various strike electrodeposition processes may be used in the method 10of FIG. 1 without departing from the scope of the present disclosure.However, disclosed is a particular tin-bismuth electrodeposition methodthat yielded an excellent substrate-to-subsequent plating bond, as shownin FIG. 2, when used in sequence with one of the disclosed activationmethods and the disclosed nickel strike plating method.

Referring to FIGS. 10 and 11, the disclosed electrodeposition method,generally designated 500, may begin at Block 502 (FIG. 10) with the stepof preparing a bath 552 containing an electrolyte solution 554, as shownin FIG. 11. The bath 552 and the activation solution 554, together withan anode 558 and a current source 560, may comprise the disclosedelectrodeposition system 550, which may be used to deposit a tin-bismuthalloy onto a substrate 556.

The substrate 556 may be a titanium substrate, such as a titaniummechanical fastener or the like. Other metallic substrates 556, such asiron substrates, copper substrates and nickel substrates (e.g.,Inconel), may also be used with the disclosed electrodeposition method500 and system 550 without departing from the scope of the presentdisclosure.

The anode 558 of the disclosed electrodeposition system 550 may be a tinanode (e.g., 99.99 percent pure tin) or a tin-bismuth anode. As onegeneral example, the anode 558 may include about 2 percent by weight toabout 5 percent by weight bismuth, with the balance substantially tin.As one specific example, the anode 558 may include about 3 percent byweight bismuth, with the balance substantially tin.

The bath 552 may be any vessel suitable for receiving and containing theelectrolyte solution 554. Compositionally, the material forming the bath552 should be chemically compatible with the activation solution 554. Ofcourse, the bath 552 should be sized and shaped to be able to receivetherein the anode 558 and the substrate 556.

The electrolyte solution 554 includes water (H₂O), a stannous saltdissolved in the water, a bismuth salt dissolved in the water, and anacid. The electrolyte solution 554 may be maintained at atmosphericpressure (e.g., 1 atm) and at a temperature between about 15° C. andabout 50° C. (e.g., room temperature (˜21° C.)). However, using higherand lower pressures, and higher and lower temperatures is contemplated,and will not result in a departure from the scope of the presentdisclosure.

The stannous salt in the electrolyte solution 554 provides stannous(tin(II)²) ions. In one formulation, the stannous salt in theelectrolyte solution 554 is stannous sulfate (SnSO₄). In anotherformulation, the stannous salt in the electrolyte solution 554 isstannous chloride (SnCl₂). In another formulation, the stannous salt inthe electrolyte solution 554 is stannous fluoride (SnF₂). In yet anotherformulation, the stannous salt in the electrolyte solution 554 includesat least two of stannous sulfate (SnSO₄), stannous chloride (SnCl₂), andstannous fluoride (SnF₂).

The stannous salt in the electrolyte solution 554 may be present at aconcentration ranging from about 15 grams per liter to about 200 gramsper liter, based on the total volume of the electrolyte solution 554. Inone alternative expression, the stannous salt concentration ranges fromabout 15 grams per liter to about 150 grams per liter, based on thetotal volume of the electrolyte solution 554. In another alternativeexpression, the stannous salt concentration ranges from about 15 gramsper liter to about 100 grams per liter, based on the total volume of theelectrolyte solution 554. In another alternative expression, thestannous salt concentration ranges from about 20 grams per liter toabout 100 grams per liter, based on the total volume of the electrolytesolution 554. In another alternative expression, the stannous saltconcentration ranges from about 20 grams per liter to about 50 grams perliter, based on the total volume of the electrolyte solution 554. In yetalternative expression, the stannous salt concentration ranges fromabout 25 grams per liter to about 35 grams per liter, based on the totalvolume of the electrolyte solution 554.

The bismuth salt in the electrolyte solution 554 provides bismuth (Bi³)ions. In one formulation, the bismuth salt in the electrolyte solution554 is bismuth sulfate (Bi₂(SO₄)₃). In another formulation, the bismuthsalt in the electrolyte solution 554 is bismuth oxide (Bi₂O₃). Inanother formulation, the bismuth salt in the electrolyte solution 554 isbismuth nitrate (Bi(NO₃)₃). In another formulation, the bismuth salt inthe electrolyte solution 554 is bismuth chloride (BiCl₃). In anotherformulation, the bismuth salt in the electrolyte solution 554 is bismuthtrifluoride (BiF₃). In yet another formulation, the bismuth salt in theelectrolyte solution 554 includes at least two of bismuth sulfate(Bi₂(SO₄)₃), bismuth oxide (Bi₂O₃), bismuth nitrate (Bi(NO₃)₃), bismuthchloride (BiCl₃), and bismuth trifluoride (BiF₃).

The bismuth salt in the electrolyte solution 554 may be present at aconcentration ranging from about 0.25 grams per liter to about 10 gramsper liter, based on the total volume of the electrolyte solution 554. Inone alternative expression, the bismuth salt concentration ranges fromabout 0.25 grams per liter to about 5 grams per liter, based on thetotal volume of the electrolyte solution 554. In another alternativeexpression, the bismuth salt concentration ranges from about 0.25 gramsper liter to about 2.5 grams per liter, based on the total volume of theelectrolyte solution 554. In another alternative expression, the bismuthsalt concentration ranges from about 0.25 grams per liter to about 1grams per liter, based on the total volume of the electrolyte solution554. In another alternative expression, the bismuth salt concentrationranges from about 0.3 grams per liter to about 0.8 grams per liter,based on the total volume of the electrolyte solution 554. In anotheralternative expression, the bismuth salt concentration ranges from about0.4 grams per liter to about 4 grams per liter, based on the totalvolume of the electrolyte solution 554. In yet alternative expression,the bismuth salt concentration ranges from about 0.4 grams per liter toabout 0.7 grams per liter, based on the total volume of the electrolytesolution 554.

The acid reduces the pH of the electrolyte solution 554. In oneformulation, the acid in the electrolyte solution 554 is sulfuric acid(H₂SO₄). In another formulation, the acid in the electrolyte solution554 is sulfamic acid (H₃NSO₃). In yet another formulation, the acid inthe electrolyte solution 554 includes both sulfuric acid (H₂SO₄) andsulfamic acid (H₃NSO₃).

The acid in the electrolyte solution 554 may be present at aconcentration ranging from about 50 milliliters per liter to about 150milliliters per liter, based on the total volume of the electrolytesolution 554. In one alternative expression, the acid concentrationranges from about 60 milliliters per liter to about 140 milliliters perliter, based on the total volume of the electrolyte solution 554. Inanother alternative expression, the acid concentration ranges from about70 milliliters per liter to about 130 milliliters per liter, based onthe total volume of the electrolyte solution 554. In another alternativeexpression, the acid concentration ranges from about 75 milliliters perliter to about 125 milliliters per liter, based on the total volume ofthe electrolyte solution 554. In another alternative expression, theacid concentration ranges from about 80 milliliters per liter to about120 milliliters per liter, based on the total volume of the electrolytesolution 554. In yet another alternative expression, the acidconcentration ranges from about 90 milliliters per liter to about 110milliliters per liter, based on the total volume of the electrolytesolution 554.

Additional components may be included in the electrolyte solution 554without departing from the scope of the present disclosure. Variouscarriers and/or additives may be included in the electrolyte solution554. As one specific, non-limiting example, the electrolyte solution 554may include TIN MAC HT STARTER A, a proprietary surfactant, which iscommercially available from MacDermid of Waterbury, Conn. As anotherspecific, non-limiting example, the electrolyte solution 554 may includeTIN MAC HT STARTER B, a proprietary source of methacrylic acid, which iscommercially available from MacDermid of Waterbury, Conn. As yet anotherspecific, non-limiting example, the electrolyte solution 554 may includeTIN MAC HT REPLENISHER, a proprietary source of dipropylene glycolmethyl ether and surfactant, which is commercially available fromMacDermid of Waterbury, Conn.

As one specific, non-limiting example, the electrolyte solution 554includes water, 30 grams per liter stannous sulfate (SnSO₄), 0.58 gramsper liter bismuth sulfate (Bi₂(SO₄)₃), 105 milliliters per litersulfuric acid (H₂SO₄), 20 milliliters per liter TIN MAC HT STARTER A, 5milliliters per liter TIN MAC HT STARTER B, and 3 milliliters per literTIN MAC HT REPLENISHER.

The electrolyte solution 554 may be manufactured in various ways withoutdeparting from the scope of the present disclosure. In one particularimplementation, the disclosed method for manufacturing the electrolytesolution 554 includes steps of (1) mixing the acid (e.g., 66 degreeBaume sulfuric acid) with water (e.g., deionized water) to yield anacidic solution, (2) dissolving the stannous salt (e.g., stannoussulfate (SnSO₄)) in the acidic solution, (3) dissolving the bismuth salt(e.g., bismuth sulfate (Bi₂(SO₄)₃)) in the solution, (4) optionallyadding one or more additives/carriers (e.g., TIN MAC HT STARTER A, TINMAC HT STARTER B and/or TIN MAC HT REPLENISHER), and (5) addingadditional water, if needed, to make up the required total volume of theelectrolyte solution 554.

At Block 504 (FIG. 10), the substrate 556 is immersed (e.g., completelyimmersed) in the electrolyte solution 554. A lead 566 may electricallycouple the immersed substrate 556 with a first terminal 562 of thecurrent source 560.

At Block 506 (FIG. 10), the anode 558 is immersed (e.g., completelyimmersed) in the electrolyte solution 554. A lead 568 may electricallycouple the immersed anode 558 with a second terminal 564 of the currentsource 560.

At Block 508 (FIG. 10), the current source 560 is actuated such that anelectric current is passed between the substrate 556 and the anode 558.The electric current will cause a tin-bismuth alloy to deposit onto thesubstrate 556.

The step of passing an electric current (Block 508) may be performed atvarious current densities without departing from the scope of thepresent disclosure. Those skilled in the art will appreciate thatcurrent density is a controllable parameter, and selection of anappropriate current density may require consideration of variousfactors, such as the duration of the passing step (Block 508), amongother factors. In one expression, the electric current passed during thepassing step (Block 508) may have a current density ranging from about10 amperes per square foot to about 80 amperes per square foot, based onthe surface area of the substrate 556. In another expression, theelectric current passed during the passing step (Block 508) may have acurrent density ranging from about 10 amperes per square foot to about50 amperes per square foot, based on the surface area of the substrate556. In another expression, the electric current passed during thepassing step (Block 508) may have a current density ranging from about20 amperes per square foot to about 40 amperes per square foot, based onthe surface area of the substrate 556. In another expression, theelectric current passed during the passing step (Block 508) may have acurrent density ranging from about 15 amperes per square foot to about30 amperes per square foot, based on the surface area of the substrate556. In yet another expression, the electric current passed during thepassing step (Block 508) may have a current density of about 30 amperesper square foot, based on the surface area of the substrate 556.

The step of passing an electric current (Block 508) may be performed forvarious durations of time without departing from the scope of thepresent disclosure. Those skilled in the art will appreciate that thecurrent duration is a controllable parameter, and selection of anappropriate duration of time may require consideration of variousfactors, such as the current density, among other factors. In oneexpression, the passing step (Block 508) may be performed for about 5minutes to about 120 minutes. In another expression, the passing step(Block 508) may be performed for about 5 minutes to about 60 minutes. Inanother expression, the passing step (Block 508) may be performed forabout 10 minutes to about 30 minutes. In another expression, the passingstep (Block 508) may be performed for about 10 minutes to about 20minutes. In yet another expression, the passing step (Block 508) may beperformed for about 15 minutes.

At Block 510 (FIG. 10), the substrate 556 is disconnected from thecurrent source 560 and removed from the electrolyte solution 554.

At Block 512 (FIG. 10), the substrate 556 may be rinsed with a rinsingfluid. As an example, the rinsing fluid may be water, such as deionizedwater.

Examples of the disclosure may be described in the context of anaircraft manufacturing and service method 1000, as shown in FIG. 12, andan aircraft 1002, as shown in FIG. 13. During pre-production, theaircraft manufacturing and service method 1000 may include specificationand design 1004 of the aircraft 1002 and material procurement 1006.During production, component/subassembly manufacturing 1008 and systemintegration 1010 of the aircraft 1002 takes place. Thereafter, theaircraft 1002 may go through certification and delivery 1012 in order tobe placed in service 1014. While in service by a customer, the aircraft1002 is scheduled for routine maintenance and service 1016, which mayalso include modification, reconfiguration, refurbishment and the like.

Each of the processes of method 1000 may be performed or carried out bya system integrator, a third party, and/or an operator (e.g., acustomer). For the purposes of this description, a system integrator mayinclude without limitation any number of aircraft manufacturers andmajor-system subcontractors; a third party may include withoutlimitation any number of venders, subcontractors, and suppliers; and anoperator may be an airline, leasing company, military entity, serviceorganization, and so on.

As shown in FIG. 13, the aircraft 1002 produced by example method 1000may include an airframe 1018 with a plurality of systems 1020 and aninterior 1022. Examples of the plurality of systems 1020 may include oneor more of a propulsion system 1024, an electrical system 1026, ahydraulic system 1028, and an environmental system 1030. Any number ofother systems may be included.

The disclosed compositions and methods may be used during any one ormore of the stages of the aircraft manufacturing and service method1000. As one example, components or subassemblies corresponding tocomponent/subassembly manufacturing 1008, system integration 1010, andor maintenance and service 1016 may be fabricated or manufactured usingthe disclosed compositions and methods. As another example, the airframe1018 may be constructed using the disclosed compositions and methods.Also, one or more apparatus examples, method examples, or a combinationthereof may be utilized during component/subassembly manufacturing 1008and/or system integration 1010, for example, by substantially expeditingassembly of or reducing the cost of an aircraft 1002, such as theairframe 1018 and/or the interior 1022. Similarly, one or more of systemexamples, method examples, or a combination thereof may be utilizedwhile the aircraft 1002 is in service, for example and withoutlimitation, to maintenance and service 1016.

The disclosed compositions and methods are described in the context ofan aircraft; however, one of ordinary skill in the art will readilyrecognize that the disclosed compositions and methods may be utilizedfor a variety of applications. For example, the disclosed compositionsand methods may be implemented in various types of vehicles including,for example, helicopters, passenger ships, automobiles, marine products(boat, motors, etc.) and the like.

Although various expressions of the disclosed compositions and methodsfor activating metallic substrates have been illustrated and described,modifications may occur to those skilled in the art upon reading thespecification. The present application includes such modifications andis limited only by the scope of the claims.

What is claimed is:
 1. An activation solution comprising: water; anammonium salt comprising a fluorine-containing anion; and sulfuric acid.2. The activation solution of claim 1 wherein the ammonium saltcomprises at least one of ammonium bifluoride and ammoniumtetrafluoroborate.
 3. The activation solution of claim 1 wherein theammonium salt is ammonium bifluoride.
 4. The activation solution ofclaim 1 wherein the ammonium salt is ammonium tetrafluoroborate.
 5. Theactivation solution of claim 1 wherein the ammonium salt is present at aconcentration ranging from about 10 grams per liter to about 150 gramsper liter, based on a total volume of the activation solution.
 6. Theactivation solution of claim 1 wherein the ammonium salt is present at aconcentration ranging from about 20 grams per liter to about 120 gramsper liter, based on a total volume of the activation solution.
 7. Theactivation solution of claim 1 wherein the ammonium salt is present at aconcentration ranging from about 40 grams per liter to about 100 gramsper liter, based on a total volume of the activation solution.
 8. Theactivation solution of claim 1 wherein the ammonium salt is present at aconcentration of about 80 grams per liter, based on a total volume ofthe activation solution.
 9. The activation solution of claim 1 whereinthe sulfuric acid is present at a concentration ranging from about 1percent by volume to about 70 percent by volume, based on a total volumeof the activation solution.
 10. The activation solution of claim 1wherein the sulfuric acid is present at a concentration ranging fromabout 2 percent by volume to about 50 percent by volume, based on atotal volume of the activation solution.
 11. The activation solution ofclaim 1 wherein the sulfuric acid is present at a concentration rangingfrom about 5 percent by volume to about 25 percent by volume, based on atotal volume of the activation solution.
 12. The activation solution ofclaim 1 wherein the sulfuric acid is present at a concentration of about10 percent by volume, based on a total volume of the activationsolution.
 13. The activation solution of claim 1 maintained atatmospheric pressure and a temperature ranging from about 15° C. toabout 50° C.
 14. A method for manufacturing the activation solution ofclaim 1, the method comprising: mixing the sulfuric acid with at least aportion of the water to yield an acidic solution; and dissolving theammonium salt in the acidic solution.
 15. A method for pretreating asubstrate prior to depositing a material thereon, the method comprising:immersing the substrate in the activation solution of claim 1 for apredetermined period of time.
 16. The method of claim 15 wherein thesubstrate is a titanium substrate, and wherein the predetermined periodof time is a time between about 5 seconds and about 120 seconds.
 17. Themethod of claim 15 wherein the substrate is a titanium substrate, andwherein the predetermined period of time is a time between about 20seconds and about 40 seconds.
 18. The method of claim 15 furthercomprising: removing the substrate from the activation solution afterthe predetermined period of time has elapsed; and after the removing,rinsing the substrate with a rinsing fluid.
 19. The method of claim 18wherein the rinsing fluid is deionized water.
 20. The method of claim 15further comprising: after the immersing, subjecting the substrate to ananodic sulfuric acid method.